The present invention relates to an optical element, light source unit, and display device. More specifically, the present invention concerns an optical element with a terminal connecting structure, having an improved yield while ensuring reliability, a light source unit using this optical element, and a display device equipped with this light source unit.
Liquid crystal display devices are installed on portable or hand-held terminals (mobile phones, notebook personal computers, etc.) and others, and they are in widespread use because of their features of being thin, lightweight, and low in power consumption. Such features of the liquid crystal display devices allow hand-held terminals to be used under various environments.
For example, in some case, the display of a hand-held terminal may be shared among a plurality of persons in a conference, and in some case, information may be inputted into the hand-held terminal at a public place such as an electric train or airplane.
In this way, performance required of the display of hand-held terminal varies depending on usage environments. For example, in the former case, since the display is shared among a plurality of persons, it is desired that the display of hand-held terminal be visible from anywhere, i.e., the view angle of the display device be as wide as possible. On the other hand, in the latter case, from the viewpoint of information conservation and privacy protection, it is desired that the view angle be no wider than allows user alone to see the display.
Therefore, it is demanded that the display of hand-held terminal, especially the view angle can be controlled to vary from a wide view angle state up to a narrow view angle state in accordance with a usage environment. A display device meeting this demand is, for example, disclosed in Japanese Unexamined Patent Application Publication No. 9-197405 (hereinafter referred to as Patent Document 1).
FIGS. 1A and 1B each schematically illustrates a conventional liquid crystal display device set forth in the Patent Document 1, wherein FIGS. 1A and 1B show a wide view angle state and narrow view angle state, respectively.
As shown in FIGS. 1A and 1B, the conventional liquid crystal display device 200 includes a liquid crystal display element 40, light source 41, first optical element 42 that substantially collimates light from the light source 41, and second optical element 43 that electrically controls diffusion/rectilinear-propagation of light emitted from the first optical element 42. The liquid crystal display device 200 is configured so that the light source 41, first optical element 42, second optical element 43, and liquid crystal display element 40 are stacked in this order from the light source side.
The liquid crystal display device 200 performs switching between a wide view angle display and narrow view angle display, by controlling rectilinear-propagation/diffusion of light entering the liquid crystal display element 40 by the second optical element 43.
In the liquid crystal display device 200 performing switching between a wide view angle display and narrow view angle display in this way, at least the optical element 43 must be inserted between the liquid crystal display element 40 and light source 41.
However, in a mobile phone, since a light source and optical element are accommodated in a very compact manner, a space for incorporating therein the optical element 43 is highly limited. In particular, because the casing trim-like frame (hereinafter referred to as a frame) of the display portion is very narrow, a terminal connecting portion between the optical element 43 and an external circuit for driving the optical element 43 has a significantly limited space.
In order to insert at least the optical element 43 between the liquid crystal display element 40 and light source 41, it is desirable that the optical element 43 be thin and lightweight. A possible method for reducing the thickness and weight of the optical element 43 is to use a film as a substrate. In this case, as in the case of a conventional liquid crystal panel, if a pair of substrates are opposed, an electrode of one of the substrates is electrically connected to an electrode of the other of the substrates via a silver paste, and the one substrate alone is electrically connected with an external circuit, then the gap in the silver paste portion increases. This undesirably causes variations in displays of the optical element 43. Therefore, when thinned substrates are to be used, it is desirable not to electrically connect the one substrate alone, but connect both of the pair of the substrates to the external circuit.
Methods for taking out respective electrodes from both of the pair of the substrates and connecting them to the external circuit, are disclosed in Japanese Unexamined Patent Application Publication No. 2001-356360 (hereinafter, Patent Document 2) and Japanese Unexamined Patent Application Publication No. 10-173304 (hereinafter, Patent Document 3).
The Patent Document 2 sets forth a structure for the connection of a liquid crystal device with an external circuit.
FIG. 2 is a plan view showing a connection structure between a liquid crystal device and external circuit, the connection structure being disclosed in the Patent Document 2. A liquid crystal panel 1 comprises a first substrate 2, second substrate 3, and cell constituted of a sealing member (not shown) interposed between the first and second substrates 2 and 3, the cell being formed by sealing therein a liquid crystal (not shown). The first substrate 2 has a first connection portion 2a formed so as to project from a portion opposed to the second substrate 3. On the surface of the first connection portion 2a, an electrode pattern (not shown) is formed and a first integrated circuit 5 is mounted. The second substrate 3 has a second connection portion 3a formed so as to project from a portion opposed to the first substrate 2. On the surface of the second connection portion 3a, there is provided an electrode pattern (not shown).
A flexible substrate 4 includes a first end portion 4a and second end portion 4d. On the first end portion 4a, an electrode pattern and connector portion (neither shown) are formed, and a second integrated circuit 6 is mounted. An electrode pattern (not shown) is also formed on the second end portion 4d. 
An electrode pattern (not shown) of the flexible substrate 4 is connected to the first substrate 2, and an electrode pattern (not shown) of the flexible substrate 4 is also connected to the second substrate 3. The flexible substrate 4 is substantially orthogonally folded at a folded portion located at the midway between the first end portion 4a and second end portion 4d. 
On the other hand, the Patent Document 3 discloses a structure for the connection of a liquid crystal device with a circuit substrate.
FIG. 3 is a schematic sectional view showing a connection method for an LCD (liquid crystal display) panel substrate and circuit substrate (FFC) [flat flexible cable], the connection method being disclosed in the Patent Document 3. An LCD panel substrate 32 comprises an upper substrate (first substrate) 21 and lower substrate (second substrate) 22, and liquid crystal (not shown) interposed therebetween, and seal portion 23 arranged therearound. A transparent electrode 24 and terminal 28 are formed on the surface of the upper substrate 21, and a conductive paste 30 is formed on the surface of the terminal 28. Similarly, a transparent electrode 25 and terminal 29 are formed on the surface of the lower substrate 22, and a conductive paste 31 is formed on the surface of the terminal 29.
Here, the side of the upper substrate 21, to be connected to the FFC is referred to as an upper tail portion 26, while the side of the lower substrate 22, to be connected to the FFC is referred to as a lower tail portion 27.
For the connection between the LCD panel substrate and FFC, firstly the upper substrate 21 and lower substrate 22 are pinched and fixed by a pinching member 20 using seal portion 23 on the sides of the upper tail portion 26 and lower tail portion 27. Then, a jig 15 having therein an opening 16 is inserted between the upper and lower tail portions 26 and 27; the space between the upper tail portion 26 and lower tail portion 27 is opened up; and a connecting terminal 13 of the FFC 10 is inserted into the opening 16. The connecting terminal 13 is covered with a covering material 12. By heating and fusing conductive pastes 30 and 31 that have been coated and hardened on the terminals 28 and 29, respectively, the terminal 28 of the upper tail portion 26, the terminal 29 of the lower tail portion 27, and the connecting portion 13 of the FFC 10 can be connected. Then, the LCD panel 32 and FFC 10 are bonded together with an adhesive tape. Thereafter, the pinching member 20 is removed and the jig 15 is removed through the opening 16 of the FFC 10.
However, the above-described conventional arts involve the following problems.
In the liquid crystal device set forth in the Patent Document 2, the taking out of electrodes in the first and second substrates is performed from two sides of the liquid crystal device. However, this undesirably widens the frame of the sides for taking out the electrode. In particular, when the liquid crystal device is incorporated into a mobile phone, a light source or optical element is accommodated in a very compact manner. As a result, the space for accommodating the optical element 43 is so small that the connection with the outside is performed by substantially one side. If the structure of the device is left unchanged, the connection with an external circuit for driving the optical element 43 would be impossible.
In the liquid crystal display device set forth in the Patent Document 3, it is attempted to establish the connection with the external circuit by opening a part of the device. However, in the case where the connecting portion with the external circuit is very narrow as in the mobile phone, there is no space for create a margin for opening. As a result, when terminals are joined to each other, there occurs seal peeling in the vicinity of the opening portion, resulting in a reduction in yield. Also, since the terminal is sandwiched between the upper tail portion and lower tail portion, the gap in the vicinity of the terminal connection portion increases by the thickness of the terminal. Hence, it is difficult to control the gap in the display surface, resulting in occurrences of variations in display. Furthermore, because of the structure such that the terminal is sandwiched between the upper and lower substrates, electrode portions near the seal material must be exposed. As a consequence, there occurs a possibility that a short circuit between electrodes will takes place and that the electrodes will become corroded because of adhesion of water or the like.